1. Field of the Invention
The present invention relates to a catalyst for steam reforming of hydrocarbon and more particularly to a catalyst for steam reforming of hydrocarbon which has superior properties such as high catalyst activity, high heat resistance and mechanical strength and long life and which can be suitably utilized, for example, in a hydrogen producing plant for fuel cells and a small size hydrogen producing plant.
2. Description of the Related Art
Hitherto, as catalysts for acceleration of steam reforming reaction comprising reacting a hydrocarbon with steam to form hydrogen, carbon monoxide, methane and carbon dioxide, there have been catalyst systems as disclosed in (1) Japanese Patent Kokoku No. 12917/78, (2) Japanese Patent Kokai No. 91844/81 and (3) Japanese Patent Kokai No. 4232/82.
The catalyst system disclosed in Japanese Patent Kokoku No. 12917/78 comprises an alumina carrier which supports metallic nickel as a catalyst active component and, as co-catalysts, metallic silver in an amount of at least 2 mg atom per 100 g of catalyst and at least one of oxides of yttrium, lanthanum, cerium, praseodymium, neodymium and samarium in an amount of at least 2 mg atom per 100 g of catalyst and at a ratio in number of atom to silver of 10 or less.
The catalyst system disclosed in the above Japanese Patent Kokai No. 91844/81 comprises rhodium and zirconium oxide.
The catalyst system disclosed in the above Japanese Patent Kokai No. 4232/82 comprises an active alumina containing 0.5-10% by weight of silica and 1% by weight or less, in terms of oxide, of an alkali metal or an alkaline earth metal and 0.05-20% by weight of ruthenium supported on the active alumina.
However, the alumina-supported catalyst systems disclosed in the first and the third patent publications suffer from the problems that they have activity at temperatures of higher than about 500.degree. C. and if the temperature is raised in order to further increase activity carbon is deposited on the catalyst and that when firing temperature is raised, surface area is conspicuously reduced resulting in reduction of catalyst activity or mechanical strength decreases due to shrinking or pressure loss of catalyst layer increases due to powdering to make the operation difficult.
With reference to the catalyst system disclosed in the second patent publication, the reaction temperature may be lower than for the above alumina supported catalyst systems, for example, 500.degree. C., but catalyst activity is not sufficient and besides steam/carbon ratio is high, namely, 24 mol/mol and thus such catalyst system is not necessarily advantageous for industrial process for reforming hydrocarbons with steam.
The inventors have already found that a catalyst system comprising rhodium metal supported on a zirconium carrier is a catalyst effective for reforming hydrocarbons with steam, which has high activity and can be controlled in the amount of formation of carbon on the catalyst. [cf. Igarashi et al: The 58th Catalyst Forum (A), 4 Ren B12, Nagoya].
This catalyst system is still not enough to be an industrial catalyst owing to its short life and insufficient activity.